The present invention generally relates to improved circuitry design on electrical systems having both A.C. and D.C. current. The circuit design is particularly useful for biasing and driving magnetic field transducers.
There are several classes of magnetic field transducers including in particular magnetostrictive and electromagnetic having a variable reluctance. In these types a polarizing magnetic field is required for proper operation of the devices. An alternating magnetic field is superposed on the polarizing field to produce a transducer output, which is then coupled into a mechanical or acoustical load. The alternating field may be continuous wave steady tone, voice modulation, or other time varying signal of interest. The polarizing field may be produced either by a permanent magnet bias in the magnetic circuit or by passing a polarizing direct current through one or more windings placed on the magnetic circuit. This invention relates to the latter method of polarization.
Since both alternating and direct currents pass through the same winding or windings of the transducer, means must be provided to de-couple the polarizing source from the signal source. A conventional prior art system for driving such magnetic field transducers is later described with reference to FIG. 1. A disadvantage of this system is that separate D.C. and A.C. supplies are required. A choke and blocking capacitor are used for de-coupling purposes with a resulting D.C. power loss in the windings of the choke. The above result in an increased size, weight and cost over the present invention. This is particularly true at low frequencies.